Lead frame

ABSTRACT

A lead frame includes a lead frame substrate made of a copper-based material, plating layers composed of nickel, palladium and gold layers laminated in this order on top faces and bottom faces of the lead frame substrate, and a roughened silver plating layer having acicular projections, provided as an outermost plating layer and covering faces of the lead frame substrate that form concavities or a through hole between the top faces and the bottom faces of the lead frame substrate. The roughened silver plating layer has a crystal structure in which the crystal direction &lt;101&gt; occupies a largest proportion among the crystal directions &lt;001&gt;, &lt;111&gt; and &lt;101&gt;. The lead frame can be manufactured with improved productivity owing to reduction in cost and operation time, and achieves remarkably high adhesion to sealing resin while keeping the total thickness of plating layers including the silver plating layer to be thin.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2019-055686 filed in Japan on Mar. 22, 2019, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION 1) Field of the Invention

The present invention relates to a lead frame for a semiconductor inwhich silver plating, as outermost plating, is applied to faces of alead frame substrate that form concavities or a through hole between topfaces and bottom faces of the lead frame substrate.

2) Description of Related Art

One of devices for mounting a semiconductor element thereon is a leadframe. Conventionally, often used are lead frames in which silverplating, as outermost plating, is applied to the entirety or a part ofthe surface of a lead frame substrate. Silver or an alloy containingsilver, however, has poor adhesion to a sealing resin. Therefore, such alead frame involves a problem in reliability, for the sealing resin iseasily peeled off the lead frame by shock or heat.

To solve this problem, there is known a technique in which the surfaceof the lead frame substrate is roughened to have concavities andconvexities by microetching, to produce a physical anchor effect,thereby improving adhesion to sealing resin.

However, a lead frame substrate often used in manufacture of a leadframe is made of a copper alloy containing silicon, to generate impurityresidue called smut if undergoing microetching process. For this reason,it is unsuitable to use the technique of roughening the surface of alead frame substrate made of a copper alloy into a roughened statehaving concavities and convexities by microetching process.

Further, in the case of a lead frame using a lead frame substrate madeof a copper alloy, it is necessary to minimize the influence ofdiffusion of copper, which exists in the underlying lead frame substratemade of a copper alloy, in order to secure good bondability with metalwires used at the time of bonding with a semiconductor element.Therefore, when a plating layer made of a precious metal or a preciousmetal alloy such as silver or an alloy containing silver is formeddirectly on a lead frame substrate made of a copper alloy without anundercoat layer being provided, it is generally necessary to make thethickness of the plating layer made of a precious metal or a preciousmetal alloy 2 μm or more.

On the other hand, in recent years, for cost reduction and sizereduction of semiconductor packages, high-density packaging upon use oflight, thin, short and small parts has been demanded. For sizereduction, plating layers are required to be made thinner. Regardingplating layers made of precious metals or precious metal alloys, theyare required to be made much thinner from the standpoint of costreduction also.

In a lead frame using a lead frame substrate made of a copper alloy, oneof the measures for reducing the thickness of a plating layer made of aprecious metal or a precious metal alloy is to form, as an undercoatlayer beneath the plating layer made of a precious metal or a preciousmetal alloy, a plating layer made of nickel or an alloy containingnickel, which prevents copper diffusion.

However, even if the plating layer made of a precious metal or aprecious metal alloy is made thin, the adhesion to the resin cannot beimproved.

As conventional art relating to these issues, Japanese Patent No.3259894 discloses, with respect to an undercoat layer beneath theplating layer made of a precious metal or a precious metal alloy, thetechnique of forming a dense and planar nickel plating layer on theentire surface of a copper alloy and then forming thereon a nickelplating layer in which crystal growth in the vertical direction is givenpriority over crystal growth in the horizontal direction to form a topsurface with concavities and convexities, thereby producing the physicalanchor effect for improving adhesion with sealing resin.

Japanese Patent No. 4853508 discloses, with respect to an undercoatlayer beneath the plating layer made of a precious metal or a preciousmetal alloy, the technique of forming, on a copper alloy, a nickelplating layer shaped to have conical projections and then formingthereon a nickel plating layer having good leveling property so thatprojections are shaped hemispherical, thereby improving adhesion tosealing resin and preventing seepage of epoxy resin component.

Japanese Patent No. 5151438 discloses the technique of forming, on anickel layer having a rough surface, a noble metal plating layercomposed of a gold layer and a silver layer.

The techniques disclosed by these patent documents are such that, forthe purpose of improving adhesion to resin, an undercoat layer is formedto have a roughened surface and that a noble metal plating layer is madeto laminate it as following the shape of the roughened surface. Asanother measure for improving adhesion to resin, it is conceivable toroughen the surface of a precious metal plating layer having beingformed as a smooth precious metal plating layer on the surface of thelead frame substrate. For this purpose, it is necessary to form thesmooth precious metal plating layer thickly before roughening itssurface.

After repeated trial and error, the present inventors have found itpossible to improve productivity by reducing cost and working time forforming a roughened surface, while keeping the total thickness of theplating layer to be thin as well as remarkably increasing adhesion tothe sealing resin.

SUMMARY OF THE INVENTION

A lead frame according to embodiment modes of the present inventionincludes: a lead frame substrate made of a copper-based material;plating layers composed of nickel, palladium and gold layers laminatedin this order on top faces and bottom faces of the lead frame substrate;and a roughened silver plating layer having acicular projections,provided as an outermost plating layer and covering faces of the leadframe substrate that form concavities or a through hole between the topfaces and the bottom faces of the lead frame substrate, wherein theroughened silver plating layer has a crystal structure in which thecrystal direction <101> occupies a largest proportion among the crystaldirections <001>, <111> and <101>.

According to the embodiment modes of the present invention, in a leadframe in which silver plating, as the outermost plating layer, isapplied to faces of a lead frame substrate that form concavities or athrough hole between top faces and bottom faces of the lead framesubstrate, it is possible to stay the total thickness of plating layersincluding the silver plating layer to be small and to remarkablyincrease adhesion to the sealing resin, while reducing cost and workingtime, to improve productivity.

These and other features of the present invention will become apparentfrom the following detailed description of the preferred embodimentswhen taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are diagrams that show one example of a lead frame accordingto a first embodiment mode of the present invention, where FIG. 1A is atop view, FIG. 1B is a bottom view and FIG. 1C is an explanatory diagramschematically showing the A-A cross section in FIG. 1A.

FIG. 2 is a plan view that shows one example of lead frames arrayed inmultiple rows according to the first embodiment mode of the presentinvention.

FIGS. 3A-3H to 3I-3J and FIGS. 3A-3H to 3H2-3J′ are explanatory diagramsthat show one example and another example of manufacturing procedure fora lead frame for mounting a semiconductor element thereon according tothe first embodiment mode of the present invention.

FIGS. 4A-4E and FIGS. 4A′-4E′ are explanatory diagrams that show oneexample and another example of manufacturing procedure for asemiconductor package using the lead frame for mounting a semiconductorelement thereon according to the first embodiment mode of the presentinvention.

FIGS. 5A-5C are diagrams that show one example of a lead frame accordingto a second embodiment mode of the present invention, where FIG. 5A is atop view, FIG. 5B is a bottom view and FIG. 5C is an explanatory diagramschematically showing a B-B cross section in FIG. 5A.

FIG. 6 is a plan view that shows one example of lead frames arrayed inmultiple rows according to the second embodiment mode of the presentinvention.

FIGS. 7A-7H to 7I-7J and FIGS. 7A-7H to 7 h 2-7J′ are explanatorydiagrams that show one example and another example of manufacturingprocedure for a lead frame for mounting a semiconductor element thereonaccording to the second embodiment mode of the present invention.

FIGS. 8A-8E and FIGS. 8A′-8E′ are explanatory diagrams that show oneexample and another example of manufacturing procedure for asemiconductor package using the lead frame for mounting a semiconductorelement thereon according to the second embodiment mode of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preceding the description of the embodiment modes, the backgroundleading to the derivation of the present invention and the operation andeffect of the present invention will be described.

The inventors of the present invention considered that, in order toimprove adhesion to sealing resin and to reduce the total thickness ofplating layers while reducing cost and working time for forming aroughened outermost surface for improved productivity, it was necessaryto form, either directly on the lead frame substrate or on a undercoatlayer with a smooth surface provided on the lead frame substrate, asilver plating layer with a roughened surface not by roughening thesurface of a smooth silver plating layer.

Then, in the process of trial and error, the inventors of the presentinvention have derived a lead frame in which a roughened silver platinglayer with acicular projections formed not by roughening the surface ofa smooth silver plating layer is provided as the outermost layercovering faces of a lead frame substrate that form concavities or athrough hole between the top faces and bottom faces of the lead framesubstrate made of a copper-based material.

In the present application, the acicular projections included in theroughened silver plating layer are defined as an aggregate of aplurality of acicular projections having a surface area ratio (here, theratio of the surface area of the roughened silver plating layer to thesurface area of the corresponding smooth surface) of 1.30 or more and6.00 or less.

It has been found that a roughened silver plating layer having acicularprojections with such a surface area ratio would make sealing resineasily flow into the roots of the individual projections of the acicularprojections, so that, when the sealing resin is cured, the large contactarea and the intricate contour can enhance the physical anchor effect.

Further, as a result of repeated trial and error by the inventors, ithas been found that a roughened silver plating layer having acicularprojections could be formed by growing a crystal structure in which theproportion of a predetermined crystal direction is high as beingdifferent from a crystal structure of a conventional smooth silverplating layer or a roughened silver plating layer formed by roughening asurface of a smooth silver plating layer, and that the roughened surfacehaving the acicular projections formed of the well-grown crystalstructure would be effective in remarkably improving adhesion to sealingresin compared with a roughened surface formed by the conventionaltechnique. In this way, the present invention has been introduced.

The lead frame of the embodiment modes of the present inventionincludes: a lead frame substrate made of a copper-based material;plating layers composed of nickel, palladium, and gold layers laminatedin this order on top faces and bottom faces of the lead frame substrate;and a roughened silver plating layer having acicular projections,provided as an outermost plating layer and covering faces of the leadframe substrate that form concavities or a through hole between the topfaces and bottom faces of the lead frame substrate, wherein theroughened silver plating layer has a crystal structure in which thecrystal direction <101> occupies a largest proportion among the crystaldirections <001>, <111> and <101>.

As in the lead frame of the embodiment modes of the present invention,if a roughened silver plating layer has acicular projections having asurface area ratio of 1.30 or more and 6.00 or less (i.e. the ratio ofthe surface area of the roughened silver plating layer to the surfacearea of the corresponding smooth surface), sealing resin would easilyflow into the roots of the individual acicular projections. Therefore,when the sealing resin is cured, the large contact area and theintricate contour can enhance the physical anchor effect, to achievegood adhesion. The directions in which the individual acicularprojections extend are not uniform; not only the upward direction andoblique directions but also the shape of bent needles are included. Ifthe individual acicular projections are randomly extended radially, theanchor effect on the sealing resin can be further enhanced.

In addition, as in the lead frame of the embodiment modes of the presentinvention, if a roughened silver plating layer with acicular projectionsprovided as the outermost layer and covering faces of a lead framesubstrate that form concavities or a through hole between the top facesand the bottom faces of the lead frame substrate made of a copper-basedmaterial is configured to have a crystal structure in which the crystaldirection <101> occupies a largest proportion among the crystaldirections <001>, <111> and <101>, such a roughened silver plating layerallows sealing resin to easily flow into its deeper portions andaccordingly exerts higher adhesion to the sealing resin than otherroughened silver plating layers such as those having roughened surfaceswith a surface area ratio (i.e. the ratio of the surface area of thesilver plating layer to the surface area of the corresponding smoothsurface) of less than 1.30 and those formed by roughening the surface ofa smooth silver plating layer having the conventional crystal structure,which is different from the crystal structure in which the crystaldirection <101> occupies a largest proportion among the crystaldirections <001>, <111> and <101>.

The roughened silver plating layer having acicular projections with acrystal structure in which the crystal direction <101> occupies alargest proportion among the crystal directions <001>, <111> and <101>according to the embodiment modes of the present invention can be formedby use of the lead frame substrate as a base.

In addition, according to the lead frame of the embodiment modes of thepresent invention, adhesion to the sealing resin can be remarkablyimproved by the roughened silver plating layer having acicularprojections with a crystal structure in which the crystal direction<101> occupies a largest proportion among the crystal directions <001>,<111> and <101>. Accordingly, in the case where a barrier plating layeris needed to be formed as an undercoat layer for preventing copperconstituting the material of the lead frame substrate from diffusingunder a high temperature environment, forming a thin and smooth barrierplating layer having a sufficient thickness for preventing diffusion ofthe base copper serves the purpose; it is not necessary to form abarrier plating layer with a roughened surface.

The roughened silver plating layer having acicular projections with acrystal structure in which the crystal direction <101> occupies alargest proportion among the crystal directions <001>, <111> and <101>can be formed by silver plating under the conditions described later,without roughening the surface of a smooth silver plating layer.

Therefore, by employing the lead frame of the embodiment modes of thepresent invention, it is possible to minimize the processing cost of theroughened surface for improved adhesion with resin, and to minimize thetotal thickness of the plating layers.

Further, in the lead frame of the embodiment modes of the presentinvention, preferably, the average diameter of crystal grains in theroughened silver plating layer is smaller than 0.28 μm.

If the average diameter of crystal grains in the roughened silverplating layer is 0.28 μm or greater, after crystals for silver platinggrow in the height direction, spaces between the crystals come to bewide and thus the surface area ratio (i.e. the ratio of the surface areaof the roughened silver plating layer to the surface area of thecorresponding smooth surface) fails to be within the range of 1.30 to6.00.

If the average diameter of crystal grains in the roughened silverplating layer is smaller than 0.28 μm, after crystals for silver platinggrow in the height direction, spaces between the crystals comes to benarrow and thus the surface area ratio (i.e. the ratio of the surfacearea of the roughened silver plating layer to the surface area of thecorresponding smooth surface) can be within the range of 1.30 to 6.00.More preferably, the roughened silver plating layer has crystal grainswith an average diameter of 0.15 μm or more and 0.25 μm or less.

In the lead frame of the embodiment modes of the present invention, anundercoat layer may be provided between the lead frame substrate and theroughened silver plating layer.

It is preferable that the shape of the acicular projections included inthe roughened silver plating layer in the lead frame of the embodimentmodes of the present invention is determined only by the roughenedsilver plating layer itself without being affected by the surface shapeof the base thereunder. The surface state of the base may be smooth orroughened. In consideration of costs such as productivity, it ispreferable that the base is prepared only by activation treatment on thesurface of the lead frame substrate, on which a roughened silver platinglayer is to be formed. In the case where the influence of diffusion ofcopper, which forms the material of the lead frame substrate, under ahigh temperature environment should be taken into consideration, it ispreferable to provide a smooth undercoat layer as a barrier platinglayer between the lead frame substrate and the roughened silver platinglayer. In this case, since it suffices to form the plating layer thinlyand smoothly to a thickness as to prevent diffusion of the base copper,a thin undercoat layer is preferable.

According to the lead frame of the embodiment modes of the presentinvention, in the case where silver plating layers including a roughenedsilver plating layer are directly formed on faces of a lead framesubstrate that form concavities or a through hole between top faces andbottom faces of the lead frame substrate without an undercoat layerbetween, the total thickness of the plating layers provided on the facesof the lead frame substrate that form concavities or a through holebetween the top faces and the bottom faces of the lead frame substrateis preferably 0.4 μm or more and 6.0 μm or less. To be specific, it ispreferable to form, on the faces of the lead frame substrate that formconcavities or a through hole between the top faces and the bottom facesof the lead frame substrate, a silver strike plating layer with athickness of 0.2 μm or more and 3.0 μm or less, more preferably 1.5 μm,and thereon to laminate a roughened silver plating layer having acicularprojections with a thickness of 0.2 μm or more and 3.0 μm or less, morepreferably 0.5 μm.

In the case where a nickel plating layer is provided as the undercoatbarrier plating layer, it is preferable that the thickness of the nickelplating layer provided on the faces of the lead frame substrate thatform concavities or a through hole between the top faces and the bottomfaces of the lead frame substrate be 0.3 μm or more and 3.0 μm or less.To be specific, it is preferable to form, on the faces of the lead framesubstrate that form concavities or a through hole between the top facesand the bottom faces of the lead frame substrate, a nickel plating layerwith a thickness of 0.3 μm or more and 3.0 μm or less, preferably 1.0μm, and thereon to laminate a roughened silver plating layer havingacicular projections with a thickness of 0.2 μm or more and 3.0 μm orless, preferably 0.5 μm.

In the case where a palladium plating layer is provided between theundercoat nickel plating layer and the roughened silver plating layer,the thickness of the palladium plating layer is preferably 0.005 μm ormore and 0.1 μm or less. To be specific, it is preferable to form apalladium plating layer with a thickness of 0.005 μm or more and 0.1 μmor less, preferably 0.01 μm, on the nickel plating layer formed on thefaces of the lead frame substrate that form concavities or a throughhole between the top faces and the bottom faces of the lead framesubstrate.

Further, in the case where a gold plating layer is provided between thetwo undercoat layers, which consist of the nickel plating layer and thepalladium plating layer, and the roughened silver plating layer, thethickness of the gold plating layer is preferably 0.0005 μm or more and0.01 μm or less. To be specific, it is preferable to form a gold platinglayer of 0.0005 μm or more and 0.01 μm or less, preferably 0.001 μm onthe nickel plating layer and the palladium plating layer formed on thefaces of the lead frame substrate that form concavities or a throughhole between the top faces and the bottom faces of the lead framesubstrate.

The roughened silver plating layer having acicular projections with acrystal structure in which the crystal direction <101> occupies alargest proportion among the crystal directions <001>, <111> and <101>in the lead frame of the embodiment modes of the present invention canbe obtained by plating upon use of a silver plating bath having a silverconcentration of 1.0 g/L to 10 g/L, which is a methanesulfonicacid-based silver plating solution, for 5 to 60 seconds at a temperatureof 55° C. to 65° C. and a current density of 3 A/dm² to 20 A/dm².

Therefore, according to the embodiment modes of the present invention,it is possible to manufacture a lead frame in which silver plating, asplating of the outermost layer, is applied to faces of the lead framesubstrate that form concavities or a through hole between the top facesand bottom faces of the lead frame substrate upon staying the totalthickness of plating layers including the silver plating layer to besmall and remarkably increasing adhesion to the sealing resin whilereducing cost and working time for forming the outermost, roughenedsurface, to improve productivity.

Hereinafter, lead frames to which the embodiment modes of the presentinvention are applied and a manufacturing method therefor will bedescribed. The present invention is not limited to the followingdetailed description unless otherwise specifically limited.

First Embodiment Mode

FIGS. 1A-1C are diagrams that show one example of a lead frame accordingto a first embodiment mode of the present invention, where FIG. 1A is atop view, FIG. 1B is a bottom view and FIG. 1C is an explanatory diagramschematically showing the A-A cross section in FIG. 1A. FIG. 2 is a planview that shows one example of lead frames arrayed in multiple rowsaccording to the first embodiment mode of the present invention. FIGS.3A-3H to FIGS. 3I-3J and FIGS. 3A-3H to FIGS. 3H2-3J′ are explanatorydiagrams that show one example and another example of manufacturingprocedure of a lead frame for mounting a semiconductor element thereonaccording to the first embodiment mode of the present invention. FIGS.4A-4E and FIGS. 4A′-4E′ are explanatory diagrams that show one exampleand another example of manufacturing procedure of a semiconductorpackage using the lead frame for mounting a semiconductor elementthereon according to the first embodiment mode of the present invention.

As shown in FIG. 1A, a lead frame 1 of this embodiment mode includes aplurality of terminals extending from four sides toward a site on whicha semiconductor element is to be mounted. As shown in FIG. 1C, aroughened silver plating layer 11 is provided as an outermost platinglayer covering faces of a lead frame substrate 10 that form concavitiesor a through hole between top faces and bottom faces of the lead framesubstrate 10 made of a copper-based material. In FIG. 1C, the referencenumeral 10 a denotes an internal connection terminal portion to beelectrically connected to the semiconductor element, the referencenumeral 10 b denotes an external connection terminal portion, thereference numeral 12 denotes a plating layer for internal connection,and the reference numeral 13 denotes a plating layer for externalconnection.

The roughened silver plating layer 11 has acicular projections having asurface area ratio of 1.30 or more and 6.00 or less (i.e. the ratio ofthe surface area of the roughened silver plating layer to the surfacearea of the corresponding smooth surface).

The roughened silver plating layer 11 has a crystal structure in whichthe crystal direction <101> occupies a largest proportion among thecrystal directions <001>, <111> and <101>.

The average diameter of crystal grains in the roughened silver platinglayer 11 is smaller than 0.28 μm.

In this embodiment mode, the roughened silver plating layer 11 is formedto have a thickness of 0.2 μm or more and 3.0 μm or less upon use thelead frame substrate 10 made of a copper-based material as a base.

As a modification of this embodiment mode, between the lead framesubstrate 10 made of a copper-based material and the roughened silverplating layer 11, an undercoat layer may be provided, to function as abarrier plating layer for preventing copper from diffusing under a hightemperature. In this case, the undercoat layer can be composed of any ofa nickel plating layer, nickel/palladium plating layers andnickel/palladium/gold plating layers, and the roughened silver platinglayer 11 is preferably formed to have a thickness of 0.2 μm or more and3.0 μm or less.

To be specific, in an exemplary case where an undercoat layer, whichfunctions as a barrier plating layer for preventing diffusion of copperwhen electrical connection with a semiconductor element is made viasolder, is composed of nickel/palladium plating layers ornickel/palladium/gold plating layers, the roughened silver plating layer11 is preferably formed to have a thickness of 0.2 μm or more and 3.0 μmor less.

Also, in the lead frame 1 of this embodiment mode, the lead framesubstrate 10 is provided with a plating layer 12 for internal connectionat sites corresponding to the internal connection terminal portions 10 aon the top faces and a plating layer 13 for external connection on thebottom faces.

Each of the plating layer 12 for internal connection and the platinglayer 13 for external connection is composed of nickel, palladium andgold layers made to laminate the lead frame substrate 10 in this order.

The lead frame 1 of this embodiment mode is configured so that, as shownin FIG. 2, the individual lead frames 1 are arrayed in multiple rows.

Next, one example and another example of manufacturing procedure of thelead frame 1 of this embodiment mode will be described in reference toFIGS. 3A-3H to FIGS. 3I-3J and FIGS. 3A-3H to FIGS. 3H2-3J′.

First, a metal plate 10 made of a copper-based material is prepared as alead frame substrate (See FIG. 3A).

Then, first resist layers R1 are formed on both surfaces of the metalplate 10 (See FIG. 3B).

Then, the first resist layer R1 on the upper surface side of the metalplate 10 is exposed and developed upon use of a glass mask carrying apredetermined pattern corresponding to internal connection terminalportions 10 a as well as the first resist layer R1 on the lower surfaceside of the metal plate 10 is exposed and developed upon use of a glassmask carrying a predetermined pattern corresponding to externalconnection terminal portions 10 b, to form first plating resist masks31-1 having openings at sites corresponding to the internal connectionterminal portions 10 a on the upper surface side of the metal plate 10and openings at sites corresponding to the external connection terminalportions 10 b on the lower surface side of the metal plate 10,respectively (See FIG. 3C).

Then, upon use of the first plating resist masks 31-1, a nickel platinglayer having a thickness of 0.3 to 3 μm, a palladium plating layerhaving a thickness of 0.005 to 0.1 μm, and a gold plating layer having athickness of 0.0005 to 0.1 μm are made to laminate the metal plate 10 inthis order at the sites corresponding to the internal connectionterminal portions 10 a on the upper surface side and at the sitescorresponding to the external connection terminal portions 10 b on thelower surface side, to form a plating layer 12 for internal connectionand a plating layer 13 for external connection (See FIG. 3D).

Then, the first plating resist masks 31-1 are removed (See FIG. 3E), andsecond resist layers R2 are formed on the both sides of the metal plate10 (See FIG. 3F).

Then, exposure and development are performed upon use of glass maskscarrying a pattern corresponding to a predetermined lead frame shape, toform etching resist masks 32 (See FIG. 3G).

Then, etching is performed on the both sides, to form the predeterminedlead frame shape (See FIG. 3H).

Then, upon use of the etching resist masks 32 on the both sides of themetal plate 10 as second plating resist masks, a silver plating layer 11having acicular projections is formed as the outermost plating layer onfaces of the metal plate 10 that form concavities or a through holebetween top faces and bottom faces of the metal plate 10 (See FIG. 3I).

Then, the resist masks 32 are removed (See FIG. 3J).

Thereby, the lead frame 1 of this embodiment mode is completed.

In the lead frame 1 manufactured in accordance with the proceduredescribed above and shown in FIGS. 3A-3J, the roughened silver platinglayer 11 having acicular projections is formed to cover only the facesthat form concavities or a through hole between the top and bottom facesof the lead frame substrate. According to the lead frame of thisembodiment, however, the roughened silver plating layer 11 may be formedto cover, in addition to the faces that form concavities or a throughhole between the top and bottom faces of the lead frame substrate, siteson the top face of the lead frame substrate 10 except the internalconnection terminal portions 10 a.

Such a type of lead frame 1 can be manufactured in the followingprocedure.

The steps from preparation of a metal plate 10 (See FIG. 3A) up toformation of second resist layers R2 on both sides of the metal plate 10(See FIG. 3F) are the same as the above-described manufacturingprocedure.

Then, upon use of an upper-side glass mask that carries a pattern inwhich light shield material has a higher concentration at portionscorresponding to sites other than the internal connection terminalportions 10 a on the top faces of the lead frame substrate 10 than atportions corresponding to the internal connection terminal portions 10 aon the top faces of the lead frame substrate 10 and upon use of alower-side glass mask that carries a pattern in which light shieldmaterial has substantially as high a concentration at portionscorresponding to the external connection terminal portions 10 b as atthe portions on the upper-side glass mask corresponding to the internalconnection terminal portions 10 a on the top faces of the lead framesubstrate 10, exposure and development are performed, to form etchingresist masks 32 (See FIG. 3G). In this situation, the etching resistmask 32 formed on the upper surface side of the metal plate 10 is suchthat the portions corresponding to the sites other than the internalconnection terminal portions 10 a on the top faces of the lead framesubstrate 10 have been subjected smaller amount of exposure than theportions corresponding to the internal connection terminal portions 10a, and thus present faster peelability in the resist stripping solution.

Then, the both sides are etched to form a predetermined lead frame shape(See FIG. 3H).

Then, of the etching resist masks 32 on the both sides of the metalplate 10, the portions of the upper-side etching resist mask 32corresponding to the sites other than the internal connection terminalportions 10 a on the top faces of the lead frame substrate 10 areremoved while the portions of the upper-side etching resist mask 32corresponding to the internal connection terminal portions 10 a and thelower-side etching resist mask 32 are left without being removed (SeeFIG. 3H2).

Then, upon use of the etching resist masks 32 on the both sides of themetal plate 10 as second plating resist masks, a silver plating layer 11having acicular projections is formed, as an outermost plating layer, onthe sites other than the internal connection terminal portions 10 a onthe top faces of the lead frame substrate 10 and on the faces that formconcavities or a through hole between the top faces and the bottom facesof the lead frame substrate 10 (See FIG. 3I′).

Then, the resist 32 are removed (See FIG. 3J′).

Thereby, a lead frame 1 of another example of this embodiment mode iscompleted as having the roughened silver plating layer 11 with acicularprojections formed not only on the faces that form concavities orthrough holes between the top faces and bottom faces of the lead framesubstrate 10 but also on the top faces of the lead frame substrate 10except at the internal connection terminal portions 10 a.

Regarding the process of forming the roughened silver plating layer 11having acicular projections as the outermost layer, the roughened silverplating layer is directly formed on the lead frame substrate 10 onlyupon activation treatment of the surface of the lead frame substrate 10or is formed on a thin and smooth nickel plating layer formed as abarrier plating layer to a thickness as to prevent diffusion of theunderlying copper. In the case where adhesiveness of the roughenedsilver plating layer 11 is unreliable, a silver strike plating layer maybe formed directly before roughened silver plating, so that theroughened silver plating layer 11 is formed thereon.

In order to form the roughened silver plating layer 11 having acicularprojections with a surface area ratio (i.e. the ratio of the surfacearea of the roughened silver plating layer to the surface area of acorresponding smooth surface) of 1.30 or more and 6.00 or less and witha crystal structure in which the crystal direction <101> occupies alargest proportion among the crystal directions <001>, <111> and <101>,the silver concentration in a silver plating bath composed of amethanesulfonic acid-based silver plating solution is set to 1.0 g/L ormore and 10 g/L or less. In particular, it is much preferable that thesilver concentration is in the range of 1.5 g/L or more and 5.0 g/L orless.

A silver concentration lower than 1.0 g/L is not preferable because theroughened silver plating film cannot be formed sufficiently. A silverconcentration higher than 10 g/L causes the film of the roughened silverplating layer to have a smooth surface, or fails to form acicular silvercrystals, and thus is not preferable.

As an alternative to the silver strike plating used to improvebondability between the base and the roughened silver plating layer 11,a plating layer of palladium or of an alloy containing palladium may beused to suitably bond the base and the roughened silver plating layer11.

Further, a plating layer of gold or of an alloy containing gold may beformed under the roughened silver plating layer 11.

In the case where the roughened silver plating layer 11 is formeddirectly on the lead frame substrate without an undercoat layer between,the thickness of the roughened silver plating layer 11 needs to be 0.2μm or more, and is preferably 0.2 μm or more and 3.0 μm or less.Further, from the viewpoint of cost, it is much preferable that thethickness is 0.3 μm or more and 1.0 μm or less.

In the case where plating layers made of nickel/palladium plating orplating layers made of nickel/palladium/gold plating are provided asundercoat layers functioning as a barrier for preventing copperdiffusion when electrical connection with a semiconductor element ismade via solder, the thickness of the roughened silver plating layer 11is preferably 0.2 μm or more and 3.0 μm or less.

Next, an exemplary manufacturing procedure for a semiconductor packageusing the lead frame 1 of this embodiment mode will be described inreference to FIGS. 4A-4E and FIGS. 4A′-4E′.

First, the lead frame 1 manufactured in accordance with themanufacturing procedure shown in FIGS. 3A-3J is prepared (See FIG. 4A).

Then, solder 14 is printed on the internal connection terminal portions10 a on the upper surface side of the lead frame 1, and a semiconductorelement 20 is mounted thereon and fixed, so that electrodes of thesemiconductor element 20 and the internal connection terminal portions10 a of the lead frame 1 are electrically connected (See FIG. 4B).

Then, a mold is used to seal, with sealing resin 15, a surrounding spaceregion except the external connection terminal portions 10 b on thelower surface side of the lead frame 1 (See FIG. 4C).

Lastly, semiconductor packages arrayed in multiple rows are singulatedby dicing, pressing or the like (See FIG. 4D).

Thereby, a semiconductor package 2 using the lead frame 1 of thisembodiment mode is obtained (See FIG. 4E).

A semiconductor package 2 using the lead frame 1 of another example ofthis embodiment mode manufactured in accordance with the procedure shownin FIGS. 3A-3H to FIGS. 3H2, 3I′ and 3J′ can be obtained bysubstantially the same procedure as described above (See FIGS. 4A′ to4E′).

Second Embodiment Mode

FIGS. 5A-5C are diagrams that show one example of a lead frame accordingto a second embodiment mode of the present invention, where FIG. 5A is atop view, FIG. 5B is a bottom view and FIG. 5C is an explanatory diagramschematically showing a B-B cross section in FIG. 5A. FIG. 6 is a planview that shows one example of lead frames arrayed in multiple rowsaccording to the second embodiment mode of the present invention. FIGS.7A-7H to FIGS. 7I-7J and FIGS. 7A-3J to FIGS. 7H2-3J′ are explanatorydiagrams that show an example and another example of manufacturingprocedure for a lead frame for mounting a semiconductor element thereonaccording to the second embodiment mode of the present invention. FIGS.8A-8E and FIGS. 8A′-8E′ are explanatory diagrams that show an exemplarymanufacturing procedure for a semiconductor package using the lead framefor mounting a semiconductor element thereon according to the secondembodiment mode of the present invention.

As shown in FIGS. 5A-5C, a lead frame 1′ of this embodiment modeincludes a pad portion 10 c for mounting a semiconductor element thereonand a plurality of terminals extending from four sides toward the padportion 10 c, and, as shown in FIG. 5C, a roughened silver plating layer11 is provided as an outermost plating layer covering faces of the leadframe substrate 10 that form concavities or a through hole between thetop faces and bottom faces of the lead frame substrate 10 made of acopper-base material. In FIG. 5C, the reference numeral 10 a denotes aninternal connection terminal portion to be electrically connected to thesemiconductor element, the reference numeral 10 b denotes an externalconnection terminal portion, the reference numeral 12 denotes a platinglayer for internal connection, and the reference numeral 13 denotes aplating layer for external connection.

The roughened silver plating layer 11 has acicular projections having asurface area ratio (i.e. the ratio of the surface area of the roughenedsilver plating layer to the surface area of a corresponding smoothsurface) of 1.30 or more and 6.00 or less.

The roughened silver plating layer 11 has a crystal structure in whichthe crystal direction <101> occupies a highest proportion among thecrystal directions <001>, <111> and <101>.

The average diameter of crystal grains in the roughened silver platinglayer 11 is smaller than 0.28 μm.

In this embodiment mode, the roughened silver plating layer 11 is formedto have a thickness of 0.2 μm or more and 3.0 μm or less upon use thelead frame substrate 10 made of a copper-based material as a base.

As a modification of this embodiment mode, between the lead framesubstrate 10 made of a copper-based material and the roughened silverplating layer 11, an undercoat layer may be provided, to function as abarrier plating layer for preventing copper from diffusing under a hightemperature. In this case, the undercoat layer can be composed of any ofa nickel plating layer, nickel/palladium plating layers andnickel/palladium/gold plating layers, and the roughened silver platinglayer 11 is preferably formed to have a thickness of 0.2 μm or more and3.0 μm or less.

To be specific, in an exemplary case where an undercoat layer, whichfunctions as a barrier plating layer for preventing diffusion of copperwhen electrical connection with a semiconductor element is made by wirebonding, is composed of a nickel plating layer, the roughened silverplating layer 11 is preferably formed to have a thickness of 0.2 μm ormore and 3.0 μm or less.

Also, in an exemplary case where an undercoat layer, which functions asa barrier plating layer for preventing diffusion of copper whenelectrical connection with a semiconductor element is made by wirebonding, is composed of nickel/palladium plating layers, the roughenedsilver plating layer 11 is preferably formed to have a thickness of 0.2μm or more and 3.0 μm or less.

Also, in the lead frame 1′ of this embodiment mode, the lead framesubstrate 10 is provided with a plating layer 12 for internal connectionat sites corresponding to the internal connection terminal portions 10 aon the top faces and a plating layer 13 for external connection on thebottom faces.

Each of the plating layer 12 for internal connection and the platinglayer 13 for external connection is composed of nickel, palladium andgold layers made to laminate the lead frame substrate 10 in this order.

The lead frame 1′ of this embodiment mode is configured so that, asshown in FIG. 6, the individual lead frames 1′ are arrayed in multiplerows.

Next, an exemplary manufacturing procedure for the lead frame 1′ of thisembodiment mode will be described.

The manufacturing procedure for the lead frame 1′ of this embodimentmode is substantially the same as the manufacturing procedure for thelead frame 1 of the first embodiment mode shown in FIGS. 3A-3H to FIGS.3I-3J, and FIGS. 3A-3H to FIGS. 3H2-3J′ and the process of forming theroughened silver plating layer 11 having acicular projections as anoutermost plating layer is also substantially the same as that in thelead frame 1 of the first embodiment mode (See FIGS. 7A-7H to FIGS.7I-7J, and FIGS. 7A-7H to FIGS. 7H2-7J′).

In the case where the roughened silver plating layer 11 is formeddirectly on the lead frame substrate without an undercoat layer between,the thickness of the roughened silver plating layer 11 needs to be 0.2μm or more, and is preferably 0.2 μm or more and 3.0 μm or less.Further, from the viewpoint of cost, it is much preferable that thethickness is 0.3 μm or more and 1.0 μm or less.

In the case where a nickel plating layer is provided as an undercoatlayer functioning as a barrier for preventing copper diffusion whenelectrical connection with a semiconductor element is made by wirebonding, the thickness of the roughened silver plating layer 11 ispreferably 0.2 μm or more and 3.0 μm or less.

In the case where nickel/palladium plating layers are provided asundercoat layers functioning as a barrier for preventing copperdiffusion when electrical connection with a semiconductor element ismade by wire bonding, the thickness of the roughened silver platinglayer 11 is preferably 0.2 μm or more and 3.0 μm or less.

Next, an exemplary manufacturing procedure for a semiconductor packageusing the lead frame 1′ of this embodiment mode will be described inreference to FIGS. 8A-8E.

First, the lead frame 1′ manufactured in accordance with themanufacturing procedure shown in FIGS. 7A-7J is prepared (See FIG. 8A).

Then, a semiconductor element 20 is mounted and fixed on the pad portion10 c on the upper surface side of the lead frame 1′ via a die bond 16,and electrodes of the semiconductor element 20 and the internalconnection terminal portions 10 a of the lead frame 1′ are electricallyconnected via bonding wires 17 (See FIG. 8B).

Then, a mold is used to seal, with sealing resin 15, a surrounding spaceregion except the external connection terminal portions 10 b on thelower surface side of the lead frame 1′ (See FIG. 8C).

Lastly, semiconductor packages arrayed in multiple rows are singulatedby dicing, pressing or the like (See FIG. 8D).

Thereby, a semiconductor package 2′ using the lead frame 1′ of thisembodiment mode is obtained (See FIG. 8E).

A semiconductor package 2′ using the lead frame 1′ of another example ofthis embodiment mode manufactured in accordance with the procedure shownin FIGS. 7A-7H to FIGS. 7H2, 7I′ and 7J′ can be obtained bysubstantially the same procedure as described above (See FIGS. 8A′ to8E′).

Embodied Example 1

A lead frame of Embodied Example 1 is an exemplary lead frame in whichthe roughened silver plating layer 11 is formed directly on faces of alead frame substrate 10 that form concavities or a through hole betweenthe top faces and bottom faces of the lead frame substrate 10 without anundercoat layer between.

In Embodied Example 1, a strip copper material having a thickness of 0.2mm and a width of 180 mm was prepared as the lead frame substrate 10(See FIG. 3A). First resist layers R1 with a thickness of 25 μm wereformed on both surfaces of the copper material (See FIG. 3B), and thefirst resist layer R1 on the upper surface side of the metal plate 10was exposed and developed upon use of a glass mask carrying apredetermined pattern corresponding to internal connection terminalportions 10 a as well as the first resist layer R1 on the lower surfaceside of the metal plate 10 was exposed and developed upon use of a glassmask carrying a predetermined pattern corresponding to externalconnection terminal portions 10 b, to form first plating resist masks31-1 having openings at sites corresponding to the internal connectionterminal portions 10 a on the upper surface side of the metal plate 10and having openings at sites corresponding to the external connectionterminal portions 10 b on the lower surface side of the metal plate 10,respectively (See FIG. 3C).

Then, upon use of the first plating resist masks 31-1, a nickel platinglayer having a thickness of 1.0 μm, a palladium plating layer having athickness of 0.01 μm, and a gold plating layer having a thickness of0.001 μm were laminated in this order at the sites corresponding to theinternal connection terminal portions 10 a on the upper surface of themetal plate 10 and at the sites corresponding to the external connectionterminal portions 10 b on the lower surface of the metal plate 10 at thesites corresponding to the external connection terminal portions 10 b,to form a plating layer 12 for internal connection and a plating layer13 for external connection (See FIG. 3D).

Then, the first plating resist masks 31-1 were removed (See FIG. 3E),and second resist layers R2 were formed on the both sides of the metalplate 10 (See FIG. 3F).

Then, exposure and development were performed upon use of glass maskscarrying a pattern corresponding to a predetermined lead frame shape, toform etching resist masks 32 (See FIG. 3G).

Then, etching was performed on the both sides, to form the predeterminedlead frame shape (See FIG. 3H).

Then, upon use of the etching resist masks 32 on the both sides of themetal plate 10 as second plating resist masks, faces of the metal plate10 that form concavities or a through hole between the top faces andbottom faces of the metal plate 10 were subjected to pretreatment withalkali and acid, and then were electroplated in the following manner.

By use of a silver plating bath with a silver concentration of 3.5 g/L,which was composed of a methanesulfonic acid-based silver platingsolution, plating was performed for 45 seconds at a current density of 5A/dm² and at a temperature of 60° C., to form a roughened silver platinglayer 11 with a thickness of about 1.5 μm having acicular projectionsand having values shown in Table 1 regarding surface area ratio (i.e.the ratio of the surface area of the roughened silver plating layer tothe surface area of a corresponding smooth surface), proportions ofcrystal directions <001>, <111> and <101>, and crystal grain diameter(average value) (FIG. 3I).

Then, the resist masks 32 were removed (See FIG. 3J), and thereby a leadframe 1 of Embodied Example 1 was completed.

Embodied Example 2

A lead frame of Embodied Example 2 is an exemplary lead frame having astructure in which, in consideration of electrical connection to asemiconductor element being made by wire bonding (gold wire or copperwire), a nickel plating layer is applied to faces of a lead framesubstrate 10 that form concavities or a through hole between the topfaces and bottom faces of the lead frame substrate 10, as an undercoatbarrier plating layer for preventing thermal diffusion of copperresiding in the lead frame substrate 10.

In Embodied Example 2, up to formation of the lead frame shape (SeeFIGS. 7A-7H) through pretreatment for electroplating on the faces of thelead frame substrate 10 that form concavities or a through hole betweenthe top faces and the bottom faces of the metal plate 10, steps werecarried out substantially in the same manner as in Embodied Example 1.In the subsequent electroplating treatment, first, by use of a nickelplating bath composed of nickel sulfamate, nickel chloride and boricacid, plating was performed for 1 minute and 30 seconds at a currentdensity of 2 A/dm², to form a nickel plating layer as a smooth undercoathaving a thickness of about 1.0 μm. Then, by use of a silver platingbath with a silver concentration of 3.5 g/L, which was composed of amethanesulfonic acid-based silver plating solution, plating wasperformed for 15 seconds at a current density of 5 A/dm² and at atemperature of 60° C., to form a roughened silver plating layer 11 witha thickness of about 0.5 μm having acicular projections and havingvalues shown in Table 1 regarding surface area ratio (i.e. the ratio ofthe surface area of the roughened silver plating layer to the surfacearea of a corresponding smooth surface), proportions of crystaldirections <001>, <111> and <101>, and crystal grain diameter (averagevalue) (See FIG. 7I). After that, the etching resist masks 32 wereremoved substantially in the same manner as in Embodied Example 1 (SeeFIG. 7J), and thereby a lead frame 1′ of Embodied Example 2 wascompleted.

Embodied Example 3

A lead frame of Embodied Example 3 is an exemplary lead frame having astructure in which, in consideration of electrical connection to asemiconductor element being made by wire bonding (gold wire or copperwire) as in the lead frame of Embodied Example 2, a nickel plating layerand a palladium plating layer were made to laminate top faces of thelead frame substrate 10 that form concavities or a through hole betweenthe top faces and bottom faces of the lead frame substrate 10, asundercoat barrier plating layers for preventing thermal diffusion ofcopper residing in the lead frame substrate 10.

In Embodied Example 3, up to formation of a nickel plating layer on thefaces of the lead frame substrate 10 that form concavities or a throughhole between the top faces and bottom faces of the metal plate 10 byelectroplating treatment, steps were carried out substantially in thesame manner as in Embodied Example 2. Then, by use of a palladiumplating bath composed of a dichloroamine-based palladium platingsolution, plating was performed for 10 seconds at a current density of 2A/dm², to form a palladium plating layer as a smooth undercoat having athickness of about 0.01 μm. Then, by use of a silver plating bath with asilver concentration of 3.5 g/L, which was composed of a methanesulfonicacid-based silver plating solution, plating was performed for 15 secondsat a current density of 5 A/dm² and at a temperature of 60° C., to forma roughened silver plating layer 11 with a thickness of about 0.6 μmhaving acicular projections and having values shown in Table 1 regardingsurface area ratio (i.e. the ratio of the surface area of the roughenedsilver plating layer to the surface area of a corresponding smoothsurface), proportions of crystal directions <001>, <111> and <101>, andcrystal grain diameter (average value) (See FIG. 7I). After that, theresist masks 32 were removed substantially in the same manner as inEmbodied Example 1 (See FIG. 7J), and thereby a lead frame 1′ ofEmbodied Example 3 was completed.

Embodied Example 4

A lead frame of Embodied Example 4 is an exemplary lead frame having astructure in which, in consideration of electrical connection to asemiconductor element being made via solder, a silver plating layer isapplied to faces of a lead frame substrate 10 that form concavities or athrough hole between the top faces and bottom faces of the lead framesubstrate 10, as an undercoat barrier plating for facilitating silverdiffusion to solder.

In Embodied Example 4, up to formation of the lead frame shape (SeeFIGS. 3A-3H) through pretreatment for electroplating on the faces of themetal plate 10 that form concavities or a through hole between the topfaces and bottom faces of the metal plate 10, steps were carried outsubstantially in the same manner as in Embodied Example 1. In thesubsequent electroplating treatment, by use of a silver plating bathcomposed of a cyan-based silver plating solution, plating was performedfor 60 seconds at a current density of 3 A/dm², to form a silver platinglayer as a smooth undercoat having a thickness of about 1.1 μm. Then, byuse of a silver plating bath with a silver concentration of 3.5 g/L,which was composed of a methanesulfonic acid-based silver platingsolution, plating was performed for 15 seconds at a temperature of 60°C. and at a current density of 5 A/dm², to form a roughened silverplating layer 11 with a thickness of about 0.6 μm having acicularprojections and having values shown in Table 1 regarding surface arearatio (i.e. the ratio of the surface area of the roughened silverplating layer to the surface area of a corresponding smooth surface),proportions of crystal directions <001>, <111> and <101>, and crystalgrain diameter (average value) (See FIG. 3I). After that, the resistmasks 32 were removed substantially in the same manner as in EmbodiedExample 1 (See FIG. 3J), and thereby a lead frame 1 of Embodied Example4 was completed.

Embodied Example 5

A lead frame of Embodied Example 5 is an exemplary lead frame having astructure in which, in consideration of electrical connection to asemiconductor element being made via solder as in the lead frame ofEmbodied Example 4, a nickel plating layer, a palladium plating layerand a gold plating layer are made to laminate top faces and faces thatform concavities or through hole between the top faces and bottom facesof the lead frame substrate 10, as undercoat barrier plating layers forpreventing diffusion of copper residing in the lead frame substrate 10.

In Embodied Example 5, up to formation of a palladium plating layer onthe faces of a metal plate 10 that form concavities or a through holebetween the top faces and bottom faces of the metal plate 10 byelectroplating treatment, steps were carried out substantially in thesame manner as in Embodied Example 3. Then, by use of a gold platingbath composed of a cyan-based gold plating solution, plating wasperformed for 10 seconds at a current density of 2 A/dm², to form a goldplating layer as a smooth undercoat having a thickness of about 0.001μm. Then, by use of a silver plating bath with a silver concentration of3.5 g/L, which was composed of a melthanesulfonic acid-based silverplating solution, plating was performed for 15 seconds at a temperatureof 60° C. and at a current density of 5 A/dm², to form a roughenedsilver plating layer 11 with a thickness of about 0.5 μm having acicularprojections and having values shown in Table 1 regarding surface arearatio (i.e. the ratio of the surface area of the roughened silverplating layer to the surface area of a corresponding smooth surface),proportions of crystal directions <001>, <111> and <101>, and crystalgrain diameter (average value) (See FIG. 3I). After that, the resistmasks 32 were removed substantially in the same manner as in EmbodiedExample 1 (See FIG. 3J), and thereby a lead frame 1 of Embodied Example5 was completed.

Comparative Example 1

A lead frame of Comparative Example 1 is an exemplary lead frame inwhich a smooth silver plating layer is formed directly on faces of alead frame substrate that form concavities or a through hole between thetop faces and bottom faces of the lead frame substrate without anundercoat layer between.

In Comparative Example 1, up to formation of the lead frame shapethrough pretreatment for electroplating on the faces that formconcavities or a through hole between the top faces and bottom faces ofthe metal plate, steps were carried out substantially in the same manneras in Embodied Example 1. In the subsequent electroplating treatment, byuse of a silver plating bath with a silver concentration of 65 g/L,which was composed of a cyan-based silver plating solution, plating wasperformed for 3 minutes at a current density of 3 A/dm², to form asilver plating layer with a thickness of 2.5 μm and having a smoothsurface. After that, the resist masks were removed substantially in thesame manner as in Embodied Example 1, and thereby a lead frame ofComparative Example 1 was completed.

Comparative Example 2

A lead frame of Comparative Example 2 is an exemplary lead frame inwhich a silver plating layer having a roughened surface with unevennessexpressed by a surface area ratio (i.e. the ratio of the surface area ofthe roughened silver plating layer to the surface area of acorresponding smooth surface) of less than 1.30 is formed on faces of alead frame substrate that form concavities or a through hole between thetop faces and bottom faces of the lead frame substrate.

In Comparative Example 2, up to formation of the lead frame shapethrough pretreatment for electroplating on the faces of the metal platethat form concavities or a through hole between the top faces and thebottom faces of the metal plate, steps were carried out substantially inthe same manner as in Embodied Example 1. In the subsequentelectroplating treatment, by use of a silver plating bath with a silverconcentration of 65 g/L, which was composed of a cyan-based silverplating solution, plating was performed for 6 minutes at a currentdensity of 3 A/dm², to form a silver plating layer with a thickness of5.0 μm and having a smooth surface. Then, the surface of the silverplating layer was subjected to microetching treatment for 2 minutes byuse of a stripping solution for silver plating, to form a roughened facewith unevenness on the surface of the silver plating layer. The silverplating layer given the roughened face with unevenness had a thicknessof 2.8 μm, which was about half the thickness of the silver platinglayer having the smooth surface. After that, the resist masks wereremoved substantially in the same manner as in Embodied Example 1, andthereby a lead frame of Comparative Example 2 was completed.

Comparative Example 3

The lead frame of Comparative Example 3 is an exemplary lead frame inwhich an undercoat layer having a roughened surface is formed on facesof a lead frame substrate that form concavities or a through holebetween the top faces and bottom faces of the lead frame substrate, anda silver plating layer is formed thereon.

In Comparative Example 3, up to formation of the lead frame shapethrough pretreatment for electroplating on the faces of the metal platethat form concavities or a through hole between the top faces and bottomfaces of the metal plate, steps were carried out substantially in thesame manner as in Embodied Example 1. In the subsequent electroplatingtreatment, first, by use of a nickel plating bath composed of nickelsulfamate, nickel chloride and boric acid, plating was performed for 7minutes and 30 seconds at a current density of 2 A/dm², to form a nickelplating layer with a thickness of about 5.0 μm and a smooth surface.Then, the surface of the nickel plating layer was subjected tomicroetching treatment for 2 minutes by use of a stripping solution fornickel plating, to form a roughened face with unevenness on the surfaceof the nickel plating layer. The nickel plating layer given theroughened face with unevenness had a thickness of 2.6 μm, which wasabout half the thickness of the nickel plating layer having the smoothsurface. Then, by use of a silver plating bath with a silverconcentration of 65 g/L, which was composed of a cyan-based silverplating solution, plating was performed for 1 minute and 30 seconds at acurrent density of 3 A/dm², to form, as following the surface shape ofthe underlying nickel plating layer, a silver plating layer with athickness of 1.5 μm and a roughened surface with unevenness havingvalues shown in Table 1 regarding surface area ratio (i.e. the ratio ofthe surface area of the roughened silver plating layer to the surfacearea of a corresponding smooth surface), proportions of crystaldirections <001>, <111> and <101>, and crystal grain diameter (averagevalue). After that, the etching resist masks were removed substantiallyin the same manner as in Embodied Example 1, and thereby a lead frame ofComparative Example 3 was completed.

The plating composition requirements (type and thickness of platinglayers, surface area ratio (i.e. ratio of surface area of (roughened orsmooth) silver plating layer to surface area of corresponding smoothsurface), proportions of crystal directions in the silver plating layer,and crystal grain size (average value)) for each of the lead frames ofEmbodied Examples 1 to 5 and Comparative Examples 1 to 3 are shown inTable 1.

It is noted that the field of view observed at 10,000× through ascanning electron microscope (SEM: Scanning Electron Microscope) wasanalyzed by an electron backscatter diffraction analyzer (EBSD: ElectronBackscatter Diffraction) so that the proportions of crystal directionswere calculated upon allowable angles for the respective directionsbeing set to 15°. Further, a diameter of a crystal grain was defined asa diameter of a circle with an area equivalent to that of the crystalgrain, which was defined by a grain boundary where the directiondifference was 15° or more.

The plating thickness of a silver plating layer was measured by an X-rayfluorescence analyzer (SFT3300 manufactured by SII), and the platingthickness of a plating layer using nickel/palladium/gold plating wasmeasured by an X-ray fluorescence analyzer (SFT3300 manufactured bySII).

The surface area ratio was measured by use of a 3D laser microscope(OLS4100 manufactured by OLYMPUS).

TABLE 1 Barrier Plating Layer Outermost Ag Plating Layer CrystalThickness Surface Proportion of Grain Surface (μm) Surface ThicknessArea Crystal Direction Diameter Example Morphology Ag Ni Pd AuMorphology (μm) Ratio <001> <111> <101> (μm) Embodied — — — — — Acicular1.5 3.1 8.7 16.3 23.6 0.1818 Example 1 Projections Embodied Smooth — 1.0— — Acicular 0.5 3.0 9.2 16.1 22.7 0.1935 Example 2 Projections EmbodiedSmooth — 1.0 0.01 — Acicular 0.6 3.1 8.8 15.9 23.2 0.2037 Example 3Projections Embodied Smooth 1.1 — — — Acicular 0.6 2.9 9.0 15.8 22.80.1865 Example 4 Projections Embodied Smooth — 1.0 0.01 0.001 Acicular0.5 3.1 8.6 16.3 23.0 0.1903 Example 5 Projections Comparative — — — — —Smooth 2.5 1.1 23.4 12.3 6.3 0.3058 Example 1 Comparative — — — — —Unevenness 2.8 1.3 22.6 14.2 7.2 0.3268 Example 2 by Etching ComparativeUnevenness — 2.6 — — Unevenness 1.5 1.3 22.9 13.8 7.0 0.3120 Example 3by Etching following Ni Layer

Evaluation of Resin Adhesiveness

A cylindrical resin mold of Φ2 mm for evaluation purpose was formed onthe roughened silver plating layer (the smooth silver plating layer inthe case of Comparative Example 1) of each of the completed lead framesof Embodied Examples 1 to 5 and Comparative Examples 1 to 3. The shearstrength of this resin was measured with a bond tester Dage Series 4000(manufactured by Dage Corporation), to evaluate resin adhesiveness.

The evaluation results of resin adhesiveness of Embodied Examples 1 to 5and Comparative Examples 1 to 3 are shown in Table 2.

TABLE 2 Process Amount of Ag Time (Set to Use (Set to 100 for 100 forAdhesion Comparative Comparative Examples Strength Example 1) Example 1)Embodied 15 25 60 Example 1 Embodied 15 50 20 Example 2 Embodied 15 5020 Example 3 Embodied 15 30 60 Example 4 Embodied 15 50 20 Example 5Comparative 10 100 100 Example 1 Comparative 11 200 200 Example 2Comparative 12 250 60 Example 3

The lead frame of Comparative Example 1, with a shear strength of 10MPa, was observed hardly to have a sufficient resin adhesiveness forpractical use.

In contrast, as shown in Table 2, each of the lead frames of EmbodiedExamples 1 to 5 had a shear strength 1.5 times the shear strength of thelead frame of Comparative Example 1, and was observed to have aremarkably improved resin adhesiveness.

On the other hand, although each of the lead frames of ComparativeExamples 2 and 3 had an improved resin adhesiveness with a shearstrength higher than the lead frame of Comparative Example 1, it wasonly 1.1 times as high as the lead frame of Comparative Example 1 andfailed to achieve a remarkable effect of improved resin adhesiveness asin the lead frames of Embodied Examples 1 to 5.

Evaluation of Productivity

Comparison was made regarding the processing time and the amount ofsilver plating required to form the surface morphology of the outermostplating layer in each of the lead frames of Embodied Examples 1 to 5 andComparative Examples 2 and 3 into the form of a plating layer having aroughened surface, to evaluate productivity. In evaluation ofproductivity, upon the processing time and the amount of use of silverplating for the lead frame of Comparative Example 1, in which a smoothsilver plating layer was formed as the outermost layer, being set to100, respectively, relative numerical values were used as evaluationvalues. In addition, since a lead frame should be subjected to platingprocess while being line-conveyed, the evaluation value of theprocessing time was calculated on the basis of the time required forforming a metal plating layer that required the longest plating time inthe plating process for the lead frame of each of Embodied Examples andComparative Examples (Embodied Example 1: roughened silver plating,Embodied Examples 2, 3, and 5: smooth nickel plating, Embodied Example4: smooth silver plating, Comparative Example 2: smooth silver plating,and Comparative Example 3: smooth nickel plating).

The evaluation results of productivity (the processing time and theamount of silver plating required to form the surface morphology of theoutermost plating layer into the form having a roughened surface) ofEmbodied Examples 1 to 5 and Comparative Examples 2 and 3 are shown inTable 2.

The lead frame of Comparative Example 2 is an example in which, afterformation of a silver plating layer with a smooth surface and athickness of about 5.0 μm, a roughened, uneven surface was formed at thesurface of the silver plating layer by microetching treatment with useof a silver plating stripping solution. The thickness of the silverplating layer with a roughened, uneven surface was 2.8 μm, which isabout half the thickness of the silver plating layer with a smoothsurface. As shown in Table 2, with the processing time being 200 and theamount of silver use being 200, the productivity was observed to be poorbecause of, in addition to the long processing time, a very high cost ofsilver, which is expensive.

The lead frame of Comparative Example 3 is an example in which, afterformation of a nickel plating layer with a smooth surface and athickness of about 5.0 μm, a roughened, uneven surface was formed at thesurface of the silver plating layer by microetching treatment with useof a nickel plating stripping solution. The thickness of the nickelplating layer with a roughened, uneven surface was 2.6 μm, which isabout half the thickness of the nickel plating layer with a smoothsurface. As shown in Table 2, with the processing time being 250 and theamount of silver use being 60, it was observed that, although the costof silver could be saved to some extent, the productivity was very poorbecause of the very long processing time.

On the other hand, as shown in Table 2, for every one of the lead framesof Embodied Examples 1 to 5, the processing time was 25 to 50 and theamount of silver use was 20 to 60. The productivity was observed to beremarkably improved with the processing time being reduced by 75 to87.5% and the amount of silver use being reduced by 70 to 90% ascompared with the lead frame of Comparative Example 2.

In addition, the lead frames of Embodied Examples 2, 3, and 5 wereobserved to achieve remarkably improved productivity with the processingtime being reduced by 80% and the amount of silver use being reduced by67% as compared with the lead frame of Comparative Example 3. Regardingthe lead frames of Embodied Examples 1 and 4, although the amount ofsilver use was about the same as the lead frame of Comparative Example3, it was significantly reduced as compared with the lead frame ofComparative Example 2. In addition, the processing time was reduced by88 to 90% as compared with the lead frame of Comparative Example 3. Inthis way, the lead frames of Embodied Examples 1 and 4 were observed toachieve remarkably improved productivity.

In the description above, “top faces of a lead frame substrate” isintended to mean faces of a lead frame substrate that are positioned ata highest level on the upper surface side, and “bottom faces of a leadframe substrate” is intended to mean faces of a lead frame substratethat are positioned at a lowest level on the lower surface side. Also,“faces that form concavities or a through hole between the top faces andbottom faces of the lead frame substrate” includes “faces (of the leadframe substrate) that form concavities in reference to the top faces onthe upper surface side”, “faces (of the lead frame substrate) that formconcavities in reference to the bottom faces on the lower surface side”and “wall faces of a through hole (in the lead frame substrate) from thetop faces to the bottom faces”.

Although the preferred embodiment modes and the embodied examples of thepresent invention have been described in detail above, the presentinvention is not limited to the embodiment modes and the embodiedexamples described above. Various modifications and substitutions may bemade to the embodiment modes and the embodied examples described abovewithout departing from the scope of the present invention.

The description has been made that, in the lead frame of the presentinvention, the material of the lead frame substrate is a copper-basedmaterial such as a copper alloy. However, a nickel-based alloy also maybe applied as the material of the lead frame substrate.

Further, in the lead frame of the present invention, as long as itsthickness does not impair the surface area ratio and the crystalstructure of the roughened surface having acicular projections, a silverplating layer or a plating layer combining nickel, palladium, and goldmay be made to laminate, as a plating layer for cover, the roughenedsilver plating layer having acicular projections provided as theoutermost layer.

1. A lead frame comprising: a lead frame substrate made of acopper-based material; and plating layers composed of nickel, palladiumand gold layers laminated in this order on a top face and a bottom faceof the lead frame substrate; and a roughened silver plating layer havingacicular projections, provided as an outermost plating layer andcovering faces of the lead frame substrate that form concavities or athrough hole between the top face and the bottom face of the lead framesubstrate, wherein the roughened silver plating layer has a crystalstructure in which the crystal direction <101> occupies a largestproportion among the crystal directions <001>, <111> and <101>.
 2. Thelead frame according to claim 1, wherein an average crystal graindiameter of the roughened silver plating layer is smaller than 0.28 μm.3. The lead frame according to claim 1, further comprising: an undercoatlayer provided between the lead frame substrate and the roughened silverplating layer.
 4. The lead frame according to claim 2, furthercomprising: an undercoat layer provided between the lead frame substrateand the roughened silver plating layer.